Anionic polymerization initiators based on alkali metal amides in combination with alkali metal salts and anionic polymerization process using these initiators

ABSTRACT

The invention relates to an anionic polymerization process using an initiator based on an alkali metal amide in combination with an alkali metal salt, as well as to the polymers obtained by this process. 
     The polymerization process according to the invention is characterized in that an initiator is used which results from the combination of an alkali metal amide selected from the group comprising sodium amide, potassium amide or lithium amide and an alkali metal salt of which the cation is selected from the group comprising potassium, lithium or sodium, the anion being selected from the group comprising the thiocyanate, nitrite, cyanide and cyanate anions. 
     These initiators make it possible to carry out the anionic polymerization or vinyl, heterocyclic and diene monomers in order to obtain special polymers or widely used polymers, with great adaptability and under advantageous economic conditions.

The present invention relates to new initiator systems for anionic polymerisation, to an anionic polymerisation process using these initiators and to the polymers obtained by this process.

The first anionic polymerisations were carried out by Wurz with ethylene oxide. However, it is especially Ziegler who deserves the credit for the explanation of the anionic polymerisation mechanism.

In this connection, it is necessary to distinguish clearly between pure anionic polymerisation, which is involved throughout the text which follows, and coordinated anionic polymerisation, which employs initiators such as salts of aluminium, of antimony and of the transition metals (for example the so-called Ziegler-Natta two-metal catalysts) and which has no bearing on the field in which the invention applies.

It has been known for a number of years that it is possible to polymerise lactones and lactams using sodium amide as the polymerisation initiator (German Pat. No. 1,960,385 and German Pat. No. 2,111,545).

Equally, Sigwalt et al. (C.R. Acad. Sci., Volume 252, pages 882-884, Session of Feb. 6, 1961) have shown that sodium amide initiates the polymerisation of propylene sulphide.

Unfortunately, the efficiency of the amide as an initiator is confined to particular monomers, especially to very easily polymerisable heterocyclic compounds such as propylene sulphide, the lactones or the lactams.

Furthermore, it has been shown by Sanderson and Hauser (JACS 71, 1595 (1949)) that it is possible to polymerise styrene using an alkali metal amide in liquid ammonia as the anionic polymerisation initiator.

Unfortunately, apart from the fact that this process suffers from the major disadvantage that it is carried out under conditions which are not industrially viable (a reaction temperature of between -30° and -70° C.), the presence of ammonia causes the premature and random termination of the polymerisation.

Other authors (German Pat. No. 2,365,439) have found that it is possible to upgrade the alkali metal amide by means of sulphoxides such as:

    φ--SO--(CH.sub.2).sub.6 --SO--φ

in which φ represents a phenyl nucleus.

However, once again the complexes of the latter only give good results with easily polymerisable monomers such as propylene sulphide.

Furthermore, these complexes are prepared under conditions which are not industrially viable (at -70° C., in liquid ammonia, followed by reaction for 10 hours at -45° C.).

Applicants has now discovered anionic polymerisation initiators which make it possible to overcome the abovementioned disadvantages and which result from the combination, in the presence of a solvent, of an alkali metal amide selected from the group comprising sodium amide, potassium amide or lithium amide and an alkali metal salt of which the cation is selected from the group comprising potassium, lithium or sodium and the anion is selected from the group comprising the thiocyanate, nitrite, cyanide or cyanate anions, the molar ratio of alkali metal amide to salt associated therewith being at least 1.

The Applicant Company has in fact found that the alkali metal salts cited above have a surprisingly pronounced upgrading effect on alkali metal amides as polymerisation initiators.

It is true that BIEHL et al. have already indicated, in Journal of Organic Chemistry, Volume 35, No. 7, 1970, page 2,454, that the combination of an alkali metal amide with a certain number of salts, including nitrites and thiocyanates, makes it possible to activate the amide in aryne condensation reactions, using dimethylamine as the solvent.

However, if the activity of a combination such as sodium amide/sodium nitrite is tested using the combination as a basic catalyst for the formation reaction of the triphenylmethyl anion from triphenylmethane in THF, which is known to be a good anionic polymerisation solvent, it is found that this combination is hardly more active than sodium amide used by itself.

It should furthermore be noted that in the organic chemistry reactions which have just been considered, a large amount of basic catalyst relative to the reactants themselves is used.

According to a preferred variant of the invention, from 1.5 to 3 mols of alkali metal amide are used per mol of alkali metal salt associated therewith. However, it is equally possible to use a large excess of amide over the salt associated therewith; for example, it is possible to use up to ten mols of amide per mol of salt associated therewith.

The solvents which can be used to prepare the initiators according to the invention must be aprotic and can be polar, slightly polar or even non-polar. It is possible to use polar solvents to the extent that their structure does not make them susceptible to the action of the complex bases used according to the invention. Thus, hexamethyl-phosphotriamide (HMPT) can be used up to about 25° C. but, for example, dimethylsulphoxide (DMSO), dimethylformamide (DMF) and N-methylpyrrolidone are degraded by the complex bases and should preferably be avoided. The polar solvents are from every point of view of little economic and industrial value in the field concerned by the invention. Other aprotic solvents of markedly lower polarity can be used, for example pyridine (ε=12.3 at 25° C.), though they can suffer degradation after a certain time, especially if the temperature is somewhat elevated.

The aprotic solvents of low polarity (of dielectric constant <10 at 25° C.) are particularly suitable for the preparation of the initiators according to the invention. Thus, linear or cyclic ethers and polyethers, such as tetrahydrofurane (THF) and dimethoxyethane (DME), give good results, generally within a very short time. The glymes are also suitable.

However, and this is a considerable advantage, the initiators according to the invention, can also be prepared easily in a non-polar solvent which can be the same solvent as that wherein, advantageously, the subsequent polymerisation is carried out. Thus it is possible to use alkanes or cycloalkanes such as hexane, heptane or cyclohexane, or arenes such as benzene or toluene.

If solvents containing ether bridges are used, it is important carefully to remove the oxygen and peroxides present, by means of known methods.

According to a second variant of the invention, the initiators are prepared using the monomer to be polymerised as the solvent. In this case, the polymerisation is carried out in bulk.

It has in fact been discovered, and this is another surprising aspect of the present invention, that the initiators according to the invention can be prepared in the absence of any solvent other than the monomer itself and that it is possible to do so without significant change in the activity of the initiator.

The initiators according to the invention can be prepared with the aid of several substantially equivalent methods because what is involved is bringing together the alkali metal amide and the associated salt in a solvent.

For example, it is possible first to introduce the solvent into the reactor, whilst stirring, then to introduce the alkali metal amide and finally to introduce the associated salt.

It is also possible to add a suspension of the alkali metal amide in a solvent to a solution-suspension of the associated salt in the same solvent or in a solvent miscible therewith.

Alternatively, the associated salt and the amide can be introduced into the reactor and the solvent can then be poured on top.

The alkali metal amide is preferably employed ground, in the form of particles whose mean size depends on the size of the polymerisation reactor, the size of the particles being preferably larger when the size of the reactor is itself large. Grinding can be effected in the presence of a small amount of an aprotic solvent of low polarity.

The alkali metal amide used can be of analytical grade or of commercial purity. It can contain a certain amount of sodium hydroxide, provided this proportion is sufficiently well known so that the initiator can be prepared with the proportions of reactants proposed above.

As regards moisture, the latter should be removed from the reactants, solvents and apparatuses used. However, it should be noted that the cost of sodium amide makes it possible to employ less thorough drying than in the preparation of the known initiators. In fact, the use of a slight excess of alkali metal amide makes it possible to remove traces of moisture quite sufficiently by reaction of the said amide with the said traces of moisture, thereby forming products which do not interfere with the initiator formation reaction or subsequently with the polymerisation reaction.

The initiator formation reaction is advantageously carried out, in certain cases, in the reactor which subsequently serves for the polymerisation, because this makes it possible to reduce the introduction of water into the apparatus. This reaction is preferably carried out at a temperature of 20° to 60° C. It is possible to use a lower temperature but the formation reaction becomes correspondingly longer and ultimately in general ceases below 0° C. It is also possible to work at a higher temperature, but in that case the danger of degradation of the alkali metal amide or of the solvent increases. It is advisable to stir the mixture.

In the majority of cases, the duration of the initiator formation reaction is at least one hour but does not exceed 4 hours. However, much longer heating may prove necessary in difficult cases.

Finally, it should be noted that the initiators according to the invention exhibit an adaptability in use which is rarely found with the previously known initiators. In fact, if, for reasons of convenience or necessity the initiator must be prepared in a solvent which is not the same as that wherein the polymerisation is subsequently carried out, difficulties are subsequently generally encountered. In fact, the polarity of the medium is affected and, for example, the micro-structure of the polymer obtained does not conform to what is expected. In contrast, the initiators according to the invention can be prepared in a first solvent, for example a solvent of low polarity, after which the said solvent is evaporated under an almost complete vacuum, and finally a second solvent, for example a non-polar solvent, in which it is desired to carry out the polymerisation, is introduced over the initiator, the properties of which have remained preserved. The invention thus makes it possible to achieve predetermined ideal conditions for carrying out the polymerisation.

Furthermore, it must be clearly recognised that the formation of the initiators according to the invention is not accompanied by any evolution of gas which could create an unnecessary or even objectionable excess pressure in the reactor. Furthermore, the initiators according to the invention are easy to prepare because the starting materials from which they are produced are in the solid state. Finally, no organic peroxide, the presence of which is extremely undesirable in activated anionic polymerisation, can result from the introduction of the associated salts, which would not normally contain a peroxide.

As with all anionic polymerisations, it is desirable to use dry reactants, dry solvents and dry apparatuses. However, this limitation, which determines the outcome of the polymerisation, applies less strictly when using the process according to the invention in view of the property of the alkali metal amide, a low cost product, of reacting with traces of moisture to give products which do not interfere with the course of the reaction.

The reaction can be terminated in a known manner, for example by introducing a protonising agent such as an alcohol (methanol or hexanol). The reaction medium is subsequently precipitated in methanol or hexane.

Purification of the solvents and of the reactants is obviously desirable. The solvents, which are the same as those wherein the complex base can be formed, and which in particular comprises the solvents of dielectric constant less than or equal to 10 at 25° C., are purified in a manner known to polymerisation specialists. Thus, for example, a distillation over solid sodium hydroxide or potassium hydroxide, followed by a distillation over sodium, can be carried out, finally finishing by drying the solvent over sodium wires. The monomers, for their part, are purified in a known and usual manner, which depends on the nature of the monomers and which can range from simple distillation to double distillation over molecular sieves, calcium hydride, an alkali metal or even a living polymer (polyisopropenyl-lithium).

The invention also relates to a polymerisation process characterised in that an initiator such as has just been described is used.

The polymerisation process according to the invention thus consists in using as the initiator the combination of an alkali metal amide with a salt selected from the group comprising the alkali metal nitrites, cyanates, thiocyanates and cyanides, in the absence or presence of a solvent.

The process according to the invention is particularly, but not uniquely, of value when an alkali metal nitrite or thiocyanate is used as the associated salt. It has in fact been discovered that for a given alkali metal amide and a given alkali metal of the associated salt, the effectiveness of the initiator increases in the sequence

    CN.sup.- <OCN.sup.- <SCN.sup.- ≃NO.sub.2.sup.-

This is a particularly surprising result if account is taken of the fact that, on the one hand, Biehl et al. (op. cit.) have only shown the ability of certain salts to boost alkali metal amides in the case of a particular reaction of organic chemistry, and only in the presence of solvents (dimethylamine) unsuitable for anionic polymerisation, and that, on the other hand, one of the preferred salts in the process according to the invention proves virtually ineffective in another reaction (triphenylmethane test) which is carried out in THF, which is one of the preferred solvents for anionic polymerisation. Anyone skilled in anionic polymerisation thus had to doubt the possibility of applying the combinations according to the invention in his field and was in no case able to foresee their good efficiency. This is all the more so since the low activity of the combinations according to the invention in the media required for the polymerisation could only be aggravated by the fact that in anionic polymerisation it is necessary to use amounts of basic initiators which are at least 1,000 times lower than in the reactions of synthetic organic chemistry.

It is also possible to combine the alkali metal amide with a mixture of activators, the respective proportions of which can vary substantially without affecting the result of the polymerisation reaction.

Furthermore, it has also been found advantageous, in particular as regards the yield, to combine an alkali metal amide with a salt of a different alkali metal. This is all the more the case if the difference between the ionic radii of the cations is large.

However, in general the selection of different cations has less influence than the selection of the associated anion.

On the other hand, the advantageous effects resulting from the selection of different cations and of preferred anions (nitrite or thiocyanate) are generally cumulative.

In fact, the preferred variants of the process according to the invention consist in using one of the following initiators:

NaHN₂, NaNO₂

NaNH₂, NaSCN

KNH₂, KNO₂

KNH₂, KSCN

NaNH₂, KNO₂

NaNH₂, KSCN

KNH₂, NaNO₂

KNH₂, NaSCN

LiNH₂, KSCN

LiNH₂, KNO₂

The monomers to which the invention is applicable are, as has already been stated, those of which it is known that they undergo polymerisation by a purely anionic mechanism or, to put it another way, which are capable of polymerising anionically by the opening of an ethylenic double bond or of a heterocyclic ring. Bearing in mind that the first anionic polymerisations date back more than a century, it will be seen that the list of these monomers is very long and that this mechanism is very well known. However, it must be clearly appreciated that this mechanism is the same regardless of whether the monomer is a heterocyclic compound or whether it exhibits ethylenic unsaturation or aldehyde unsaturation (which can be considered as a two-atom heterocyclic structure), because the initiation gives rise, by scission of a bond, to the formation of an active centre which, regardless of the nature of the atom which carries the negative charge, attacks a fresh molecule of monomer which in turn carries the negative charge and so on, until the monomer is exhausted or the reaction is terminated. On this subject, reference may be made, for example, to the work by Professor Georges Champetier "Chimie Macromoleculaire" ("Macromolecular Chemistry"), Volume I, Editions Hermann, Paris (1969).

However, the following monomers may be mentioned as relevant monomers, without pretending that this list is exhaustive:

In the case of vinyl monomers, those of the general formula ##STR1## R₁ =R₂ =R₃ =H and R₄ =alkyl ##STR2## where X=H, Cl, --OCH₃ or --C(CH₃)₃ ##STR3## (where R'=alkyl or cycloalkyl), or ##STR4## (where R"=alkyl) ##STR5## (where

R=alkyl, especially methyl, or aryl, especially phenyl), or

R₁ =R₂ =H,

R₃ =--CH₃ and

R₄ =phenyl, cyano or ##STR6## (R'=alkyl or cycloalkyl).

In the case of the heterocyclic monomers, the alkylene oxides, the alkylene sulphides, the lactones, the lactams, the thiethanes and the cyclic carbonates, such as ethylene oxide, propylene oxide, propylene sulphide, β-propiolactone, ε-caprolactone, pivalolactone, ε-caprolactam, propylene glycol carbonate, neopentylglycol carbonate and the like.

In the case of the conjugated diene monomers, those of the general formula: ##STR7## where:

R₁ =R₂ =R₃ =R₄ =R₅ =R₆ =H (1,3-butadiene)

R₁ =R₂ =R₄ =R₅ =R₆ =H and R₃ =alkyl or aryl

R₁ =R₂ =R₃ =R₄ =R₅ =H and R₆ =alkyl, aryl, nitrile or nitro

R₁ =R₂ =R₅ =R₆ =H and R₃ =R₄ =--CH₃

R₁ =CH₃ and R₂ =R₃ =R₄ =R₅ =R₆ =H or alkyl

R₁ =R₃ =R₄ =R₅ =H and R₁ =R₆ =phenyl

In the case of the dienes with ethylenic double bonds which are not directly conjugated: divinylbenzene, substituted cyclohexadienes such as 3,3,6,6-tetramethyl-1,2,4,5-hexadiene and vinyl or allyl carbonates of polyols or of polyether-polyols, such as allyl-diglycol carbonate.

The process according to the invention is applicable to homopolymerisation reactions and to copolymerisation reactions, either of monomers of the same family or of monomers of different families.

The polymerisation process according to the invention is carried out under conventional conditions as regards the atmosphere which must be present in the reactor; thus, the reaction is carried out in vacuo or under an atmosphere of an inert gas such as nitrogen or argon.

The temperature at which the polymerisation is carried out is not necessarily the same as that at which the initiator has been prepared, and can be between -80° C. and +70° C.

Furthermore, the temperature can be varied during the polymerisation, and this is of particular value in copolymerisations which are carried out to give a certain distribution of copolymerised species or a particular microstructure or more rapid reaction kinetics.

The amount of initiator required by the process obviously depends generally on the mean molecular weight which it is desired to achieve. For example a molar ratio of amide/monomer of the order of 0.1 to 1% can be used, but it should be emphasised that a higher ratio can be used, all the more so since the amide is relatively inexpensive.

The duration of the polymerisation reaction depends on a very large number of factors and varies from a few seconds to 24 and even 48 hours.

In the examples which follow, and which are given by way of illustration of the invention and must not be considered as limiting the scope of the latter, particular emphasis has been given to the variety of possibilities offered by the initiators according to the invention, as well as to the numerous variants of the process which are mentioned in the preceding description. Other aspects which integrally form part of the invention are also described in the said examples below.

EXAMPLE OF PREPARATION OF THE INITIATORS

A reaction flask which has been dried beforehand is swept with argon, and 25×10⁻³ mol of NaNH₂ and 16.6×10⁻³ mol of an alkali metal salt (NaNO₂, NaSCN, NaCN or KSCN) in 20 ml of solvent such as THF or toluene are then introduced. The whole is heated for 2 hours at 50° C. The solvent is either retained, if it is desired to carry out the anionic polymerisation in the same solvent, or is removed if it is desired to carry out the anionic polymerisation in bulk or in a different solvent.

All the initiators are prepared in accordance with the same process.

EXAMPLES 1 TO 20: ANIONIC POLYMERISATION OF STYRENE

10⁻¹ mol of styrene is introduced into the reaction flask in which the initiator has been prepared. The solution is then heated for a given time, after which the reaction is stopped by precipitating the polymer by means of methanol. The results obtained are summarised in the tables which follow:

Table 1

The experiments were carried out in 20 ml of toluene, using sodium amide as the alkali metal amide, and an activator. R is the molar ratio of amide/activator.

    __________________________________________________________________________      No.                                                                               ACTIVATOR  T  0° C.                                                                       Yield                                                                              ##STR8##                                                                           ##STR9##                                                                           ##STR10##                                    __________________________________________________________________________     1  KNO.sub.2 3mM (R = 6)                                                                     18 h                                                                              50° C.                                                                      33% 3,000                                                                              20,000                                                                             6.7                                           2  NaCN 3mM (R = 6)                                                                          18 h                                                                              50°  C.                                                                     11% 4,000                                                                              50,000                                                                             12                                            3  NaSCN 8mM (R = 6)                                                                         24 h                                                                              60° C.                                                                       5% 13,000                                                                             75,000                                                                             6                                             4  NaNO.sub.2 3mM (R = 6)                                                                    18 h                                                                              50° C.                                                                      45% 5,500                                                                              12,000                                                                             2.2                                           5  NaSCN 3mM (R = 6)                                                                         18 h                                                                              50° C.                                                                      49% 3,000                                                                              10,000                                                                             3.3                                           __________________________________________________________________________

Table 2

The experiments were carried out in 20 ml of toluene, using potassium amide as the alkali metal amide, and an activator, at a temperature of 50° C. for 18 hours. R is the molar ratio of amide/activator.

    ______________________________________                                          No.  ACTIVATOR      Yield                                                                                  ##STR11##                                                                            ##STR12##                                                                            ##STR13##                             ______________________________________                                         6    KCN 3mM (R = 2)                                                                               27%     2,650  5,500                                                                               2                                      7    KOCN 3mM (R= 2)                                                                               15%     4,000 45,000                                                                               11                                     8    KSCN 3mM (R = 2)                                                                              30%     4,500 45,000                                                                               10                                     9    NaNO.sub.2 3mM (R = 6)                                                                        45%     5,600 11,950                                                                               2.1                                    10   NaSCN 3mM (R = 6)                                                                             49%     3,000  9,600                                                                               3.2                                    11   KNO.sub.2 3mM (R = 6) 33%                                                                     3,140   18,900                                                                               6.0                                          12   NaCN 3mM (R = 6)                                                                              11%     4,040 53,150                                                                               3.1                                    ______________________________________                                    

Table 3

The experiments were carried out in 40 ml of THF, using 16×10⁻³ mol of sodium amide and 8×10⁻³ mol of activator, at a temperature of 50° C.

    ______________________________________                                          No.  VATORACTI-                                                                               T        Yield                                                                                ##STR14##                                                                            ##STR15##                                                                            ##STR16##                           ______________________________________                                         13   KSCN      6 h      100%  28,000                                                                               400,000                                                                              14                                   14   NaNO.sub.2                                                                              22 h      100%  12,000                                                                                80,000                                                                              6.7                                  15   KNO.sub.2                                                                                5 h      100%  60,000                                                                               650,000                                                                              11                                   16   KCN      24 h       90%  10,000                                                                                20,000                                                                              2                                    17   NaCN     24 h       11%  45,000                                                                               450,000                                                                              10                                   18   KOCN     20 h       3%   14,500                                                                               100,000                                                                              7                                    19   NaSCN     7 h 30    56%   6,500                                                                                50,000                                                                              8                                    20   KSCN     24 h       4%   20,000                                                                                73,000                                                                              3.7                                       (alone)                                                                   ______________________________________                                    

EXAMPLES 21 TO 47: ANIONIC POLYMERISATION OF 2-VINYLPYRIDINE Table 4

The experiments were carried out with 10 ⁻¹ mol of 2-vinylpyridine in 20 ml of toluene, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 40° C.

    ______________________________________                                          No.    ACTIVATOR     T        Yield                                                                                  ##STR17##                               ______________________________________                                         21     NaNO.sub.2     4 h     50%     4,100                                    22     KNO.sub.2      5 h     58%     5,600                                    23     NaSCN         18 h     60%     4,800                                    24     KCNO          18 h     53%     3,900                                    25     NaCNO         18 h     50%     3,000                                    26     NaCN          18 h     39%     2,200                                    ______________________________________                                    

Table 5

The experiments were carried out with 10⁻¹ mol of 2-vinylpyridine in 20 ml of THF, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 40° C.

    ______________________________________                                          No.    ACTIVATOR     t        Yield                                                                                  ##STR18##                               ______________________________________                                         27     NaNO.sub.2     4 h     60%     4,900                                    28     KNO.sub.2      4 h     70%     7,300                                    29     NaSCN         18 h     65%     4,300                                    30     KCNO          18 h     62%     4,000                                    31     NaCNO         18 h     60%     3,700                                    32     NaCN          18 h     57%     3,000                                    ______________________________________                                    

Table 6

The experiments were carried out with 10⁻¹ mol of 2-vinylpyridine, without a solvent, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 40° C.

    ______________________________________                                          No.    ACTIVATOR     t        Yield                                                                                  ##STR19##                               ______________________________________                                         33     NaNO.sub.2    1 h      60%     4,600                                    34     KNO.sub.2     1 h      57%     6,300                                    35     NaSCN         3 h      48%     5,000                                    36     KCNO          3 h      52%     4,800                                    37     NaCNO         3 h      39%     4,000                                    38     NaCN          5 h      28%     3,700                                    ______________________________________                                    

Table 7

The experiments were carried out with 10⁻¹ mol of 2-vinylpyridine, using 25×10⁻³ mol of alkali metal amide and 12.5×10⁻³ mol of activator in 30 ml of different solvents, at a temperature of 40° C. for 18 hours.

    ______________________________________                                          No.    ACTIVATOR    SOLVENT     Yield                                                                                 ##STR20##                              ______________________________________                                         39     NaNO.sub.2   Hexane      47%    4,000                                   40     NaCNO        Hexane      40%    3,800                                   41     NaCN         Hexane      33%    2,900                                   42     NaNO.sub.2   Pyridine    25%    1,700                                   43     NaCN         Pyridine    20%    1,500                                   44     NaCN         DME         68%    7,000                                   45     NaNO.sub.2   DME         70%    6,700                                   46     NaCNO        DME         63%    5,300                                   ______________________________________                                    

EXAMPLES 47 TO 66: ANIONIC POLYMERISATION OF α-METHYLSTYRENE

The procedure is the same as for styrene. The results obtained are summarised in the tables which follow:

Table 8

The polymerisation experiments were carried out with 10⁻¹ mol of α-methylstyrene in 20 ml of toluene, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 40° C. for 4 hours.

    ______________________________________                                          No.     ACTIVATOR      Yield                                                                                      ##STR21##                                  ______________________________________                                         47      NaNO.sub.2     45%         450                                         48      KNO.sub.2      50%         700                                         49      NaSCN          30%         520                                         50      KCNO           30%         420                                         51      NaCN           10%         300                                         52      NaCNO          25%         360                                         53      NaCN            9%         310                                         ______________________________________                                    

Table 9

The experiments were carried out with 10⁻¹ mol of α-methylstyrene in 20 ml of THF, using 25×10⁻³ mol of sodium amide and 12×10⁻³ mol of activator, at a temperature of 40° C. for 4 hours.

    ______________________________________                                          No.     ACTIVATOR      Yield                                                                                      ##STR22##                                  ______________________________________                                         54      NaNO.sub.2     40%         600                                         55      KNO.sub.2      55%         830                                         56      NaSCN          37%         500                                         57      KCNO           35%         380                                         58      NaCN           17%         340                                         59      NaCNO          30%         400                                         60      NaCN           23%         335                                         ______________________________________                                    

Table 10

The polymerisation experiments were carried out with 10⁻¹ mol of α-methylstyrene, without a solvent, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 40° C.

    ______________________________________                                          No.    ACTIVATOR    t         Yield                                                                                  ##STR23##                               ______________________________________                                         61     NaNO.sub.2    4 h      60%     800                                      62     KNO.sub.2     4 h      47%     1,200                                    63     NaSCN        18 h      35%     680                                      64     KCNO         18 h      38%     590                                      65     NaCNO        18 h      35%     610                                      66     NaCN         18 h      30%     420                                      ______________________________________                                    

EXAMPLES 67 TO 102: ANIONIC POLYMERISATION OF ACRYLONITRILE

The procedure is the same as for styrene. The results obtained are summarised in the tables which follow.

Table 11

The polymerisation experiments were carried out with 5×10⁻² mol of acrylonitrile, without a solvent, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 35° C.

    ______________________________________                                          No.    ACTIVATOR    t         Yield                                                                                  ##STR24##                               ______________________________________                                         67     NaNO.sub.2   10 mins   80%     5,000                                    68     KNO.sub.2    15 mins   88%     5,500                                    69     NaSCN        20 mins   75%     4,600                                    70     KCNO         15 mins   80%     3,900                                    71     NaCNO        15 mins   80%     4,200                                    72     NaCN         20 mins   70%     3,800                                    ______________________________________                                    

Table 12

The experiments were carried out with 5×10⁻² mol of acrylonitrile in 20 ml of THF, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 40° C.

    ______________________________________                                          No.    ACTIVATOR    T         Yield                                                                                  ##STR25##                               ______________________________________                                         73     NaNO.sub.2   20 mins   100%    6,300                                    74     KNO.sub.2    20 mins   100%    7,000                                    75     NaSCN        20 mins   100%    4,200                                    76     KCNO         1 h        90%    5,400                                    77     NaCNO        1 h        90%    4,900                                    78     NaCN         1 h        90%    4,700                                    ______________________________________                                    

Table 13

The experiments were carried out with 5×10⁻² mol of acrylonitrile in 20 ml of toluene, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 40° C.

    ______________________________________                                          No.    ACTIVATOR    T         Yield                                                                                  ##STR26##                               ______________________________________                                         79     NaNO.sub.2   30 mins   90%     4,000                                    80     KNO.sub.2    30 mins   88%     4,700                                    81     NaSCN        40 mins   80%     3,800                                    82     KCNO         1 h       87%     2,900                                    83     NaCNO        1 h       79%     3,300                                    84     NaCN         2 h       63%     2,400                                    ______________________________________                                    

Table 14

The experiments were carried out with 5×10⁻² mol of acrylonitrile in 20 ml of THF, using 25×10⁻³ mol of LiNH₂ and 12.5×10⁻³ mol of activator, at a temperature of 40° C. for 18 hours.

    ______________________________________                                          No.     ACTIVATOR      Yield                                                                                      ##STR27##                                  ______________________________________                                         85      NaSCN          20%         2,700                                       86      NaNO.sub.2     25%         5,200                                       87      KCNO           17%         4,300                                       88      KNO.sub.2      35%         6,200                                       89      NaCNO          15%         4,000                                       90      NaCN           10%         2,500                                       ______________________________________                                    

Table 15

The experiments were carried out with 5×10⁻² mol of acrylonitrile, without a solvent, using 25×10⁻³ mol of lithium amide and 12.5×10⁻³ mol of activator, at a temperature of 40° C. for 18 hours.

    ______________________________________                                          No.     ACTIVATOR      Yield                                                                                      ##STR28##                                  ______________________________________                                         91      NaSCN          38%         5,800                                       92      NaNO.sub.2     40%         6,400                                       93      KCNO           45%         7,000                                       94      KNO.sub.2      68%         9,300                                       95      NaCNO          40%         6,000                                       96      NaCN           22%         2,900                                       ______________________________________                                    

Table 16

The experiments were carried out with 5×10⁻² mol of acrylonitrile in 20 ml of toluene, using 25×10⁻³ mol of lithium amide and 12.5×10⁻³ mol of activator, at a temperature of 40° C. for 18 hours.

    ______________________________________                                          No.     ACTIVATOR      Yield                                                                                      ##STR29##                                  ______________________________________                                          97     NaSCN          20%         4,000                                        98     NaNO.sub.2     15%         2,900                                        99     KCNO           12%         3,600                                       100     KNO.sub.2      28%         4,200                                       101     NaCNO          10%         3,200                                       102     NaCN            7%         1,850                                       ______________________________________                                    

EXAMPLES 103 TO 114: POLYMERISATION OF METHYL METHACRYLATE

The procedure is the same as for styrene. The results obtained are summarised in the table which follow.

Table 17

The experiments were carried out with 10⁻¹ mol of methyl methacrylate in 30 ml of THF, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 35° C.

    ______________________________________                                          No.  VATORACTI-                                                                                Time   %Yield                                                                               ##STR30##                                                                            ##STR31##                                                                             ##STR32##                           ______________________________________                                         103  NaNO.sub.2 18 h   100   14,000                                                                               22,000 1.56                                      12.5 × 10.sup.-3                                                         mol                                                                       104  KNO.sub.2   2 h   100   12,400                                                                               25,700 2.1                                       12.5 × 10.sup.-3                                                         mol                                                                       105  NaSCN       3 h   100   10,000                                                                               25,000 2.5                                       12.5 × 10.sup.-3                                                    106  KCNO       11/2 h 100   41,100                                                                               109,300                                                                               2.66                                      12.5 × 10.sup.-3                                                         mol                                                                       ______________________________________                                    

Table 18

The experiments were carried out with 10⁻¹ mol of methyl methacrylate in 30 ml of toluene, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 35° C.

    ______________________________________                                          No.  VATORACTI-                                                                                Time   %Yield                                                                               ##STR33##                                                                            ##STR34##                                                                             ##STR35##                           ______________________________________                                         107  NaNO.sub.2 2 h    100   41,000                                                                               195,600                                                                               4.77                                      12.5 × 10.sup.-3                                                         mol                                                                       108  KNO.sub.2  2 h    100   27,700                                                                                82,600                                                                               2.98                                      12.5 × 10.sup.-3                                                         mol                                                                       109  NaSCN      2 h    100   19,000                                                                                87,000                                                                               1.95                                      12.5 × 10.sup.-3                                                         mol                                                                       110  KCNO       11/2 h 100   61,600                                                                               254,400                                                                               4.13                                      12.5 × 10.sup.-3                                                         mol                                                                       ______________________________________                                    

Table 19

The experiments were carried out with 10⁻¹ mol of methyl methacrylate, without a solvent, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator.

    __________________________________________________________________________      No.                                                                               ACTIVATOR                                                                               °C.                                                                        Time                                                                               %Yield                                                                             ##STR36##                                                                          ##STR37##                                                                           ##STR38##                                     __________________________________________________________________________     111                                                                               NaNO.sub.2                                                                              35 45 mins                                                                            100 33,600                                                                             113,000                                                                             3.36                                              12.5 × 10.sup.-3 mol                                                  112                                                                               KNO.sub.2                                                                               40 30 mins                                                                            100 24,600                                                                              45,600                                                                             1.86                                              12.5 × 10.sup.-3 mol                                                  113                                                                               NaSCN    40 55 mins                                                                            100 13,700                                                                              24,500                                                                             1.79                                              12.5 × 10.sup.-3 mol                                                  114                                                                               KCNO     35 15 mins                                                                            100 47,000                                                                             138,400                                                                             2.95                                              12.5 × 10.sup.-3 mol                                                  __________________________________________________________________________

Microstructure determinations were carried out on the product which results from the polymerisation of methyl methacrylate using sodium amide and an associated salt as the initiator.

The results are shown in the table below.

Table 20

    ______________________________________                                                          NMR                                                           ACTIVATOR  SOLVENT     T        H      S                                       ______________________________________                                         NaNO.sub.2 THF         11.8     56.6   31.5                                    NaSCN      THF         21.1     53.9   25.0                                    NaNO.sub.2 Toluene     36.5     44     19.5                                    KNO.sub.2  Toluene     26.5     52.1   21.4                                    KCNO       Toluene     22.4     51.7   25.9                                    ______________________________________                                    

EXAMPLES 115 TO 140: POLYMERISATION OF METHACRYLONITRILE

The procedure is the same as for styrene. The results obtained are summarised in the tables which follow.

Table 21

The experiments were carried out with 10⁻¹ mol of methacrylonitrile in 30 ml of THF, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 35° C.

    ______________________________________                                          No.  ACTIVATOR    °C.                                                                             Time   Yield %                                                                                ##STR39##                            ______________________________________                                         115  NaNO.sub.2   35      10 mins                                                                               100     20,000                                     12.5 × 10.sup.-3 mol                                                116  KNO.sub.2    35      15 mins                                                                               90      16,000                                     12.5 × 10.sup.-3 mol                                                117  NaSCN        35      30 mins                                                                               80      12,000                                     12.5 × 10.sup.-3 mol                                                118  KCNO         35      10 mins                                                                               90      17,000                                     12.5 × 10.sup.-3 mol                                                ______________________________________                                    

Table 22

The polymerisation experiments were carried out with 10⁻¹ mol of methacrylonitrile in 30 ml of toluene, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 35° C.

    ______________________________________                                          No.  ACTIVATOR        Time     Yield %                                                                               ##STR40##                               ______________________________________                                         119  NaNO.sub.2 12.5 × 10.sup.-3 mol                                                           20 mins  85     18,000                                   120  KNO.sub.2 12.5 × 10.sup.-3 mol                                                            35 mins  98     14,000                                   121  NaSCN 12.5 × 10.sup.-3 mol                                                                30 mins  95     10,000                                   122  KCNO 12.5 × 10.sup.-3 mol                                                                 30 mins  90     12,500                                   ______________________________________                                    

Table 23

The experiments were carried out with 10⁻¹ mol of methacrylonitrile, without a solvent, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 35° C.

    ______________________________________                                          No.  ACTIVATOR        Time     Yield %                                                                               ##STR41##                               ______________________________________                                         123  KNO.sub.2 12.5 × 10.sup.-3 mol                                                             5 mins  100    38,000                                   124  KCNO 12.5 × 10.sup.-3 mol                                                                 15 mins  100    32,000                                   125  NaNO.sub.2 12.5 × 10.sup.-3 mol                                                           10 mins  100    29,000                                   126  NaSCN 12.5 × 10.sup.-3 mol                                                                20 mins  100    35,000                                   ______________________________________                                    

Table 24

The experiments were carried out with 5×10⁻² mol of methacrylonitrile, without a solvent, using 25×10⁻³ mol of lithium amide and 12.5×10⁻³ mol of activator, at a temperature of 40° C. for 8 hours.

    ______________________________________                                          No.     ACTIVATOR     Yield %                                                                                    ##STR42##                                   ______________________________________                                         127     NaSCN         40          6,000                                        128     NaNO.sub.2    48          7,200                                        129     KNO.sub.2     75          10,500                                       130     NaCNO         45          6,300                                        131     NaCN          30          3,200                                        132     KCNO          50          8,100                                        ______________________________________                                    

Table 25

The experiments were carried out with 5×10⁻² mol of methacrylonitrile in 20 ml of solvent, using 25×10⁻³ mol of lithium amide and 12.5×10⁻³ mol of activator, at a temperature of 40° C. for 18 hours.

    ______________________________________                                          No.    ACTIVATOR   SOLVENT    Yield %                                                                                ##STR43##                               ______________________________________                                         133    NaSCN       THF        25      3,000                                    134    NaNO.sub.2  THF        28      6,200                                    135    KCNO        THF        19      5,100                                    136    KNO.sub.2   THF        40      73,000                                   137    NaSCN       Toluene    23      4,300                                    138    NaNO.sub.2  Toluene    16      3,700                                    139    KCNO        Toluene    14      4,000                                    140    KNO.sub.2   Toluene    30      5,000                                    ______________________________________                                    

EXAMPLES 141 TO 152: POLYMERISATION OF ISOPRENE

The procedure is the same as for styrene. The results are summarised in the tables below.

Table 26

The experiments were carried out with 10⁻¹ mol of isoprene in 20 ml of THF, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ of activator, at a temperature of 40° C. for 18 hours.

    ______________________________________                                          No.      ACTIVATOR      Yield                                                                                     ##STR44##                                  ______________________________________                                         141      KNO.sub.2      12%        1,500                                       142      NaNO.sub.2     10%          800                                       143      KCNO           10%        1,000                                       144      NaCNO           9%        1,300                                       145      NaSCN          10%        1,200                                       146      NaCN            5%        1,100                                       ______________________________________                                    

Table 27

The experiments were carried out with 10⁻¹ mol of isoprene, without a solvent, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator, at a temperature of 40° C. for 18 hours.

    ______________________________________                                          No.      ACTIVATOR      Yield                                                                                     ##STR45##                                  ______________________________________                                         147      KNO.sub.2      10%        2,500                                       148      NaNO.sub.2     10%        2,000                                       149      KCNO           10%        1,500                                       150      NaCNO          10%        1,300                                       151      NaSCN          10%        1,400                                       152      NaCN           10%          900                                       ______________________________________                                    

EXAMPLES 153 to 158: POLYMERISATION OF HETEROCYCLIC COMPOUNDS Table 28

The experiments were carried out using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of activator.

    __________________________________________________________________________      No.                                                                               Monomer  vatorActi-                                                                          Solvent                                                                             t  0° C.                                                                       Yield                                                                              ##STR46##                                    __________________________________________________________________________     153                                                                               ethylene oxide                                                                          NaNO.sub.2                                                                          toluene                                                                             18 h                                                                              40° C.                                                                      100%                                                                               6,000                                            0.19 mol      30 ml                                                         154                                                                               ethylene oxide                                                                          NaNO.sub.2                                                                          --   18 h                                                                              25° C.                                                                      100%                                                                               4,500                                            0.20 mol                                                                    155                                                                               cyclic carbonate                                                                        NaSCN                                                                               --    2 h                                                                              25° C.                                                                      100%                                                                               10,000                                           of 2-ethyl-2-                                                                  butyl-propane-                                                                 1,3-diol                                                                       5.4 × 10.sup.-2 mol                                                   156                                                                               cyclic carbonate                                                                        NaSCN                                                                               toluene                                                                             24 h                                                                              25° C.                                                                      100%                                                                               6,800                                            of 2-methyl-2-                                                                 propyl-propane-                                                                1,3-diol                                                                       6.3 × 10.sup.-2 mol                                                   __________________________________________________________________________

The experiments carried out with propylene oxide, using 25×10⁻³ mol of sodium amide and 12.5×10⁻³ mol of sodium cyanide for 48 hours at 25° C. show a substantial increase in the molecular weight. The results are summarised in Examples 161 and 162.

    ______________________________________                                                     SOLVENT                                                                                      ##STR47##                                            ______________________________________                                         Example 157  THF 20 ml        7,500                                            Example 158  without solvent 12,500                                            ______________________________________                                    

EXAMPLES 159 to 163: ANIONIC POLYMERISATION CARRIED OUT USING, AS THE INITIATOR, AN ALKALI METAL AMIDE AND A MIXTURE OF ASSOCIATED SALTS Table 29

The procedure is the same as for styrene. The results are summarised in the table below.

The experiments were carried out with 10⁻¹ mol of methyl methacrylate, in a solvent or without a solvent, using 25×10⁻² mol of lithium amide and a mixture of associated salts as the activator, at a temperature of 40° C.

    ______________________________________                                          No.  ACTIVATOR      SOLVENT    T    Yield                                                                                ##STR48##                           ______________________________________                                         159  NaSCN +  NaNO.sub.2                                                                           THF        18 h 25%   4,500                                     6 × 10.sup.-3  6 × 10.sup.-3                                  160  NaSCN + NaCNO  THF        18 h 23%   5,000                                     2 × 10.sup.-3  10.sup.-3                                            161  KNO.sub.2 + KCNO                                                                              Toluene    18 h 22%   4,500                                     5 × 10.sup.-3  7 × 10.sup.-3                                  162  KNO.sub.2 + NaCN                                                                              Toluene    18 h 25%   3,900                                     9 × 10.sup.-3  3 × 10.sup.-3                                  163  KNO.sub.2 + NaCNO                                                                             --          8 h 30%   4,500                                     5 × 10.sup.-3  7 × 10.sup.-3                                  ______________________________________                                    

EXAMPLES 164 to 175: ANIONIC POLYMERISATION IN THE ABSENCE OF AN ALKALI METAL AMIDE

The procedure is the same as for styrene. The results obtained are summarised in the table below.

Table 30

The experiments were carried out with 10⁻¹ mol of methyl methacrylate in 20 ml of solvent or without a solvent, using exclusively 12.5×10⁻³ mol of activator. All the experiments proved negative.

    ______________________________________                                                   ACTIVATOR SOLVENT                                                    ______________________________________                                         164         NaNO.sub.2  toluene                                                165         KCNO        toluene                                                166         KNO.sub.2   toluene                                                167         NaSCN       toluene                                                168         KNO.sub.2   THF                                                    169         NaNO.sub.2  THF                                                    170         KCNO        THF                                                    171         NaSCN       THF                                                    172         KNO.sub.2   --                                                     173         NaNO.sub.2  --                                                     174         NaSCN       --                                                     175         KCNO        --                                                     ______________________________________                                    

EXAMPLES 176 TO 181: POLYMERISATION OF STYRENE IN TOLUENE

88 mM of styrene were polymerised, in 8 hours, in 40 ml of toluene at 40° C. in the presence of 25 mM of NaNO₂ and of an amount of NaNH₂ corresponding to the molar ratio indicated in column 2 of Table 31, which table also shows the results obtained:

Table 31

    ______________________________________                                          Example                                                                                ##STR49##  Yield (%)                                                                               ##STR50##                                                                             ##STR51##                                                                             I *                                 ______________________________________                                         176     1          80       101,000                                                                               292,900                                                                               2.9                                  177     2          100       95,600                                                                               210,300                                                                               2.2                                  178     4          77        64,200                                                                               173,300                                                                               2.7                                  179     6          58        41,430                                                                               128,430                                                                               3.1                                  180     10         40        13,300                                                                                59,850                                                                               4.5                                  181     12         40        10,000                                                                                48,000                                                                               4.8                                  ______________________________________                                          *measured by GPC at 30° C. in THF.                                

It is found that the best yields are obtained with a ratio of about 2 but variation of the proportion of amide provides a means of achieving an Mn of between 100,000 and 10,000.

EXAMPLES 182 TO 186: BULK POLYMERISATION OF STYRENE

88 mM of styrene were polymerised at 40° C. for one hour in the presence of 25 mM of NaNO₂ and of an amount of NaNH₂ corresponding to the molar ratio indicated in column 2 of Table 32, which table shows the results obtained.

Table 32

    ______________________________________                                          Example                                                                                ##STR52##  Yield (%)                                                                               ##STR53##                                                                             ##STR54##                                                                             I (*)                               ______________________________________                                         182     1          85       45,500 409,500                                                                               9                                    183     2          100      53,400 341,750                                                                               6.4                                  184     4          87       42,600 404,700                                                                               9.5                                  185     6          85       37,500 412,500                                                                               11                                   186     10         80       23,600 283,200                                                                               12                                   ______________________________________                                          (*)measured by GPC at 30° C. in THF.                              

It is found that in bulk polymerisation, as in solution polymerisation, the highest results are obtained for a ratio of about 2 and that it is possible to vary Mn by varying the proportion of NaNH₂.

EXAMPLES 187 TO 193: POLYMERISATION OF STYRENE IN THF

88 mM of styrene were polymerised for 4 hours in 40 ml of THF in the presence of 8.3 mM of NaNO₂ and 16.7 mM of NaNH₂. The polymerisation was carried out at various temperatures between -80° C. and +40° C. The results obtained are shown in Table 33.

Table 33

    ______________________________________                                          Example                                                                                °C.                                                                              (%)Yield                                                                                ##STR55##                                                                              ##STR56##                                                                             (*)I                                 ______________________________________                                         187      40      100       35,700 151,500                                                                               2                                     188      20      100       85,000 161,500                                                                               1.9                                   189       0      100       87,000 165,300                                                                               1.9                                   190     -20      100      110,000 187,000                                                                               1.7                                   191     -40      100      120,000 180,000                                                                               1.5                                   192     -60      100      137,000 205,500                                                                               1.5                                   193     -80      100      175,000 262,500                                                                               1.5                                   ______________________________________                                    

It is found that the yields are excellent at all temperatures and that when the polymerisation temperature decreases, the polydispersity index decreases whilst the molecular weights increase.

EXAMPLES 194 TO 200: POLYMERISATION OF STYRENE IN SOLUTION

88 mM of styrene were polymerised for 4 hours in the presence of 16.7 mM of NaNH₂ and 8.3 mM of NaNO₂ in various solvents. The polymerisation temperature was 40° C. (except for HMPT, where it was 20° C.). The results obtained are given in Table 34.

Table 34

    ______________________________________                                          Example                                                                               Solvent    (%)Yield                                                                                ##STR57##                                                                             ##STR58##                                                                             (c) (*)I                             ______________________________________                                         194    HMPT (d)   100      42,000  50,400                                                                               1.2                                   195    THF        100      75,700 151,500                                                                               1.3                                   196    DME        100      85,000 110,500                                                                               1.3                                   197    diglyme    100      123,000                                                                               221,400                                                                               1.8                                   198    toluene     45      55,600 122,300                                                                               2.2                                   199    benzene     40      41,300  95,000                                                                               2.3                                   200    cyclohexane                                                                                8       10,000  51,000                                                                               5.1                                   ______________________________________                                          (*) measured by GPC in THF at 30° C.                              

It is found that the polymerisation medium is another possible means of selection of the molecular weights.

EXAMPLES 201 TO 208: BULK POLYMERISATION OF STYRENE

88 mM of styrene were polymerised for 4 hours at 40° C. (20° C. only in Example 202) in the presence of 8.3 mM of NaNO₂ and 16.7 mM of NaNH₂ and in the absence of solvent.

The initiator was prepared in various solvents which were then evaporated to dryness (Examples 202 to 208), or the monomer was simply run onto the salts which had been ground together (Example 201).

The results obtained are shown in Table 35.

Table 35

    ______________________________________                                                            Yield    Mn     Mp                                          Example Solvent    (%)      (*)    (*)    I                                    ______________________________________                                         201     --         100      173,100                                                                               917,450                                                                               5.3                                  202     HMPT       100       74,400                                                                               290,150                                                                               3.9                                  203     THF        100      133,600                                                                               587,850                                                                               4.4                                  204     DME        100      128,750                                                                               527,900                                                                               4.1                                  205     diglyme    100      141,200                                                                               663,650                                                                               4.7                                  206     toluene     95      103,600                                                                               507,650                                                                               4.9                                  207     benzene     98      101,900                                                                               509,500                                                                               5.0                                  208     cyclohexane                                                                                90       99,900                                                                               479,500                                                                               4.8                                  ______________________________________                                          (*) measured by GPC in THF at 30° C.                              

EXAMPLES 209 TO 232: POLYMERISATION OF METHYL METHACRYLATE IN THF

All the polymerisations shown below were carried out at 35° C. for 2 hours in 30 ml of THF with 100 mM of methyl methacrylate in the presence of 16.7 mM of amide and 8.3 mM of associated salt.

Tables 36, 37 and 38 show the results obtained respectively with LiNH₂, NaNH₂ and KNH₂.

Table 36

    ______________________________________                                          Example                                                                                Activator                                                                                %Yield                                                                                  ##STR59##                                                                             ##STR60##                                                                              I*                                  ______________________________________                                         209     NaNO.sub.2                                                                               57       34,400 72,240 2.1                                   210     NaSCN     50       29,500 67,850 2.3                                   211     NaCNO     38       19,550 52,800 2.7-212 NaCN 35 17,500 43,750 2.5                                              8                                     213     KNO.sub.2 64       28,800 54,700 1.9                                   214     KSCN      59       24,800 52,100 2.1                                   215     KCNO      45       15,100 37,750 2.5                                   216     KCN       40       12,000 27,600 2.3                                   ______________________________________                                           *measured by GPC at 30°  C. in THF.                              

Table 37

    ______________________________________                                          Example                                                                                Activator                                                                                %Yield                                                                                  ##STR61##                                                                             ##STR62##                                                                             I*                                   ______________________________________                                         217     NaNO.sub.2                                                                               100      43,500 56,550 1.3                                   218     NaSCN     100      22,000 46,200 2.1                                   219     NaCNO      96      19,200 48,000 2.5                                   220     NaCN       90      16,200 38,900 2.4                                   221     KNO.sub.2 100      18,000 23,400 1.3                                   222     KSCN      100      15,000 28,500 1.9                                   223     KCNO      100      13,000 29,900 2.3                                   224     KCN       100      10,000 22,000 2.2                                   ______________________________________                                           *measured by GPC at 30°  C. in THF.                              

Table 38

    ______________________________________                                          Example                                                                                Activator                                                                                %Yield                                                                                  ##STR63##                                                                             ##STR64##                                                                              I*                                  ______________________________________                                         225     NaNO.sub.2                                                                               100      23,700 28,450 1.2                                   226     NaSCN     100      23,000 34,500 1.5                                   227     NaCNO     100      21,000 44,100 2.1                                   228     NaCN      100      19,000 34,200 1.8                                   229     KNO.sub.2 100      12,700 19,050 1.5                                   230     KSCN      100      11,000 20,900 1.9                                   231     KCNO      100       8,200 18,850 2.3                                   232     KCN       100       7,500 18,000 2.4                                   ______________________________________                                          *measured by GPC at 30° C. in THF.                                

As far as is known, polymethyl methacrylate having a polydispersity index of between 1.2 and 1.6 and a number-average molecular weight of between 12,000 and 45,000 was not previously known.

EXAMPLES 233 TO 256: BULK POLYMERISATION OF STYRENE

All the polymerisations shown below were carried out at 45° C. for 2 hours, without a solvent, with 88 mM of styrene poured onto 16.7 mM of amide and 8.3 mM of associated salt which had been ground together.

Tables 39, 40 and 41 show the results respectively obtained with LiNH₂, NaNH₂ and KNH₂.

Table 39

    ______________________________________                                          Example                                                                                Activator                                                                               Yield %                                                                                  ##STR65##                                                                             ##STR66##                                                                              I*                                  ______________________________________                                         233     NaNO.sub.2                                                                               15       36,000 140,400                                                                               3.9                                   234     NaSCN     10       21,000 90,300 4.3                                   235     NaCNO     10       16,000 81,600 5.1                                   236     NaCN       7        9,300 454,500                                                                               4.9                                   237     KNO.sub.2 20       15,600 60,850 3.9                                   238     KSCN      15        9,300 38,150 4.1                                   239     KCNO      15        7,800 41,350 5.3                                   240     KCN       20        1,600  7,500 4.7                                   ______________________________________                                          *measured by GPC at 30° C. in THF.                                

Table 40

    ______________________________________                                          Example                                                                                Activator                                                                               Yield %                                                                                  ##STR67##                                                                             ##STR68##                                                                              I*                                  ______________________________________                                         241     NaNO.sub.2                                                                               55       104,500                                                                               376,200                                                                               3.6                                   242     NaSCN     60       102,000                                                                               357,000                                                                               3.5                                   243     NaCNO     45       54,000 226,800                                                                               4.2                                   244     NaCN      40       42,000 222,600                                                                               5.3                                   245     KNO.sub.2 60       33,600 110,900                                                                               3.3                                   246     KSCN      55       21,450  87,950                                                                               4.1                                   247     KCNO      50       10,000  38,000                                                                               3.8                                   248     KCN       45        2,700  14,850                                                                               5.5                                   ______________________________________                                           *measured by GPC at 30° C. in THF.                               

Table 41

    ______________________________________                                          Example                                                                                Activator                                                                               Yield %                                                                                  ##STR69##                                                                             ##STR70##                                                                              I*                                  ______________________________________                                         249     NaNO.sub.2                                                                               70       98,000 294,000                                                                               3.0                                   250     NaSCN     55       56,400 236,800                                                                               4.2                                   251     NaCNO     65       52,000 192,400                                                                               3.7                                   252     NaCN      50       31,000 99,200 3.2                                   253     KNO.sub.2 75       22,500 92,250 4.1                                   254     KSCN      60        9,600 30,700 3.2                                   255     KCNO      60        6,000 18,600 3.1                                   256     KCN       55        2,750 10,450 3.8                                   ______________________________________                                           *measured by GPC at 30° C. in THF.                               

Particularly high values of Mn were obtained.

EXAMPLE 257: COPOLYMERIZATION OF STYRENE AND METHYL METHACRYLATE IN SOLUTION

The initiator was prepared by reacting 17 mM of NaNH₂ with 8,5 mM of NaNO₂ in 100 ml of THF, during 2 hours at 40° C.

The reactor containing the initiator was cooled at -20° C. and 88 mM of styrene were then introduced on the initiator. After one hour one half of the formed polystyrene was taken. This polymer which was "killed" when a small amount of methanol, had a Mn equal to 42,500, i.e., to the theoritical Mn value.

On the second half which remained in the reactor, 20 mM of methyl methacrylate (MAM) were introduced and let polymerize during one hour, the temperature of -20° C. being still maintained. The obtained copolymer has a Mn of 58800: the poly MAM had therefore a Mn of 16300 (whereas the theoritical value was 20,000) (yield: 80%).

The Mn were measured by Gel Permeation Chromatograhy (GPC) at 30° C., in THF.

EXAMPLE 258: MASS COPOLYMERIZATION OF STYRENE AND METHYL METHACRYLATE

The initiator was prepared in the same way as in example 257 in about 50 ml of THF. The THF was then evaporated and 88 mM of styrene were introduced upon the initiator at -30° C., during one hour. One half of the formed polystyrene was taken and showed a Mn equal to 13,400 (yield 100%). On the remaining half, 100 mM of MAM were then introduced and the mixture was allowed to stand at -30° C. for one hour. The copolymer thus obtained had a Mn equal to 30 900 (theory: 46 000). The yield of the copolymerization of the MAM was 54%. The Mn were measured by Gel Permeation Chromatography at 30° C., in THF. 

We claim:
 1. Process for the polymerisation of vinyl or diene monomers capable of polymerising anionically by opening of an ethylenic double bond, wherein the reaction is initiated, in the presence of an aprotic solvent, by means of an initiator which is the product of the reaction of an alkali metal amide which is a member selected from the group consisting of sodium amide, potassium amide and lithium amide and at least one alkali metal salt of which the cation is a member selected from the group consisting of potassium, lithium, and sodium, the anion being a member selected from the group consisting of the thiocyanate, cyanate, cyanide and nitrite anions, in a molar ratio of alkali metal amide/associated salt at least equal to 1 up to
 12. 2. Anionic polymerisation process according to claim 1, wherein the molar ratio of alkali metal amide/associated salt is between 1.5 and
 3. 3. Anionic polymerisation process according to claim 1, wherein the reaction is initiated in the presence of a solvent of dielectric constant less than 10 at 25° C.
 4. Anionic polymerisation process according to claim 1, 2, or 3 wherein the solvent is the monomer to be polymerised.
 5. Anionic polymerisation process according to anyone of claims 1, 2, or 3 wherein the initiator is the reaction product of:(a) NaNH₂ and NaNO₂ (b) NaNH₂ and NaSCN (c) KNH₂ and KNO₂ (d) KNH₂ and KSCN (e) NaNH₂ and KNO₂ (f) NaNH₂ and KSCN (g) KNH₂ and NaNO₂ (h) KNH₂ and NaSCN (i) LiNH₂ and KSCN or (j) LiNH₂ and KNO₂. 